The invention relates to the provision of a valve assembly that may be used to throttle and close off the flow of abrasive fluids. According to the invention, a ball valve member is provided having a tubular insert of abrasive-resistant material and a particular dimension, said insert providing surfaces for cutting off the flow of abrasive fluid through the valve. Tubular inserts of abrasive resistant material on either side of the ball valve member conduct fluid to and from the ball valve and cooperate with the valve member insert. The diameter of the passageway through the ball valve member insert is preferably relatively small compared to the diameter of the ball itself so that only a small angle of deflection is provided during throttling, which is important in reducing the abrasive action of the fluid. Also, a passageway may be provided between the ball valve and the body, and the ball valve and the inlet tubular insert whereby a purge fluid under a pressure higher than the pressure of fluid flowing through the valve may be injected in the passageways therebetween. There are many prior art teachings of valves having particular means associated therewith so that the valves may better withstand the action of fluids flowing therethrough, such as shown in U.S. Pat. Nos. 867,780; 885,526; 925,809; 3,073,336; and 3,825,030. Such valves often take the form of plug members formed entirely of ceramic material for resisting the corrosive action of fluid flowing therethrough, such as shown in U.S. Pat. Nos. 867,780; 885,526; and 925,809. The plug valves provide a cylindrical seat of relatively large area, thus large seating contact pressure is difficult to arrange, whereas in ball valves which seal in a seat of circular form, large contact pressure is easy to arrange. It is advantageous to provide the relatively rotatable parts of a valve of metal for proper operation, which provision is not suggested by the all-ceramic valves in the above-mentioned patents. Other prior patents which show ball valves provide plastic coatings therefor, such as U.S. Pat. Nos. 3,073,336 and 3,825,030. The coatings are provided on all wetted surfaces of the valves, and since coatings are provided a large range of materials with desirable properties are precluded from use therein, such as boron carbide.
In general, the prior art valves that are concerned with protection against fluid action are concerned with protection against corrosive chemical action of the fluid rather than the abrasive action of fluid. Therefore, such prior art valves in general have a very large angle of deflection during throttling. When abrasive fluids are to be valved, however, it is important to keep the angle of deflection as small as possible since the abrasive action of the fluid increases as the angle of deflection increases. This is accomplished by making the diameter of the passageway in the abrasive-resisting material insert much less than the diameter of the ball valve. Also, since tubular inserts are provided instead of coatings, a wide range of very abrasive-resistant materials that are not available in coating form -- such as boron carbide -- may be provided. Also, all wetted surfaces need not be formed of the abrasive-resistant material, whereas when chemical corrosion protection is desired all wetted surfaces must be formed of corrosion resistant material.
According to the present invention a ball valve assembly is provided including a main body portion having inlet and outlet bores therein, a generally spherical ball valve member in the body member and having a bore therethrough, tubular inserts of abrasive-resistant material provided in the bores, the tubular inserts having passageways therein, and the arcuate surfaces of the insert in the ball member having an arc length greater than the diameter of the passageways in the inlet and outlet inserts and the outlet insert having an arcuate portion of a length greater than or equal to the diameter of the passageway in the valve member insert. Also, the diameter of the ball compared to the diameter of the passageways is preferably selected so that the angle of deflection of the fluid during throttling is very small. Also, gaps are provided between the ball and the body and the ball and the inlet insert so that purge fluid under high pressure may be injected therein.
It is the primary object of this invention to provide a relatively inexpensive valve with improved abrasive-resisting properties for the throttling and valving of abrasive fluids. This and other objects of the invention will become clear upon an inspection of the detailed description of the invention and from the appended claims.